1. Field of the Invention
This invention relates to an apparatus for discriminating a light source and, more particularly, to an apparatus for determining whether or not the light source which is to be used for illuminating an object to be shot or photographed with a video camera or an electronic still camera is a source of fluorescent light.
2. Description of the Prior Art
In shooting or photographing with a video camera or an electronic still camera, it is necessary is dependent upon a light source used for illuminating the object and to adjust the white balance. The adjustment of the white balance is dependent upon the measured color temperature. It is therefore necessary to identify the kind of the light source used for illuminating the object. In addition, since flicker occurs in the light emitted from the light source having spectrum peaks in the energy distribution thereof, it is also necessary, for example, to adjust the shutter speed of the camera to not less than 1/60 second for shooting a still image.
For meeting such requirements, a device for determining whether or not the light source is a fluorescent light source is disclosed in the Japanese Patent Laid-Open Publication No. 61-240790. As disclosed in the publication, for example, the fluorescent light source is identified by detecting whether the light intensity of the light source is changed at a frequency of 100 to 120 Hz. As it is known that the light intensity of the fluorescent light source is changed at that frequency range that fact can be used to identify the light source as fluorescent. Recently, however, a high-frequency lighting system has become popular as the lighting system for fluorescent lamps whereby flicker is reduced by switching lighting at a frequency of some hundred kHz. Since the brightness ripple is reduced under this system of the light source, the fluorescent light source cannot be determined accurately with the abovementioned prior-art device.